Nuclear matter and finite nuclei: recent studies based on Parity Doublet Model

In this review, we summarize recent studies on nuclear matter and finite nuclei based on parity doublet models. We first construct a parity doublet model (PDM), which includes the chiral invariant mass $m_0$ of nucleons together with the mass generated by the spontaneous chiral symmetry breaking. We then study the density dependence of the symmetry energy in the PDM, which shows that the symmetry energy is larger for smaller chiral invariant mass. Then, we investigate some finite nuclei by applying the Relativistic Continuum Hartree-Bogoliubov (RCHB) theory to the PDM. We present the root-mean-square deviation (RMSD) of the binding energies and charge radii, and show that $m_0$ = 700 MeV is preferred by the nuclear properties. Finally, we modify the PDM by adding the iso-vector scalar meson $a_0(980)$ and show that the inclusion of the $a_0(980)$ enlarges the symmetry energy of the infinite nuclear matter.